Circuit designers are always in need for new circuitry for generating pulses of various widths, shapes and amplitudes. It is often desired to provide circuits that produce a first pulse of one duration and amplitude followed by another pulse of a second duration and amplitude or a train of pulses at a first frequency followed by a train of pulses of a second frequency.
One such practical application resides in controlling a telephone switching matrix made up of columns and rows of interconnected coil forms, each of which includes a pair of switching elements in the form of a pair of sealed remanent magnetic reed contacts that are selectively operated by a pair of differentially wound coils. In the normal execution of telephone office switching functions, coil forms in a matrix are selectively operated by concurrent energization of both differential windings of a coil form positioned in a particular row and column. Subsequent switch selection signals are in many cases impressed through both column (vertical) and row (horizontal) windings of already selected (closed) reed contacts such that additional magnetic forces are produced to flex the reed contacts which tend to rub and can ultimately stick together.
In order to alleviate stuck contacts being encountered in a switch select operation, the switch select pulse is preceded by a release pulse which functions to energize the vertical differentially wound coils to positively release the contacts prior to receipt of a select pulse. In order to maximize energy utilization it is desired that the pre-release pulse be of a relatively high amplitude and narrow width with respect to the subsequently applied operate or switch selection pulse. The concept of utilizing pre-release pulses in matrix switch selection sequences is further described in U.S. Pat. No. 3,859,471 issued to Danielsen et al. on Jan. 7, 1975, which discloses separate pulse generating circuits that are sequentially operated to generate a release pulse followed by an operate pulse.